The invention relates to a cardboard blank for a gas-tight and liquid-tight folding box, especially one bearing external printing, which carries on the inner side, especially on an aluminum foil laminated thereto, a layer of heat-sealable plastic covering the entire surface.
In folding boxes prepared from cardboard blanks, the cardboard gives the box stiffness, and the plastic covering makes the box liquid-tight. In order also to make the box liquid-tight at points subject to particularly great stress, e.g., at corners and edges and in the area of seams or at lines scored for tearing, the inside of the box is covered with a relatively thick layer of plastic, which is polyethylene as a rule. Thick plastic coverings, however, are undesirable both from the viewpoint of costs and from the viewpoint of fabrication. The creasing of the blank is made difficult by the resilient properties of the plastic covering, and folding is opposed by a greater tendency to spring back.
Whenever the folding box is to be not merely liquid-tight but also light-tight and gas-tight, an aluminum foil is placed between the cardboard and the plastic covering.